1. Field of the Invention
The present invention relates to a photo-detection device wherein an infrared light or visible light radiated from or reflected by a surface of an object to be detected is guided to and detected at a position separated from the object through an optical fiber, and a temperature distribution detection device using the same to form a temperature distribution image or a visible image of a surface of the object.
2. Description of the Related Art
There is a conventional image capture method for forming an image of an object at a narrow place to which a man cannot access in an atomic power generation plant, for example. Such a method is shown in a Japanese Patent Application KOKAI Publication No. 05-293779, for example. According to the described method, a mirror supported by a supporting mechanism is inserted in the narrow place to extract an image light of the object to an external, so that an image of the object in the narrow place is captured optically. The direction of the mirror should be changed when an image of a desired position in the narrow place is to be captured. In order to change the mirror direction, it is necessary to provide a driving mechanism in the mirror supporting mechanism, thereby rendering the device be bulky. Moreover, since the driving mechanism should be provided with a movable part, the tolerance of movement of the movable part is limited at a very narrow place, thereby disabling the image capture of a desired object.
Further, there is a demand for inspecting a heat generation status of electronic parts mounted on a given mounted circuit board (a printed circuit board on which electronic elements are mounted is called as the mounted circuit board) in a state where a plurality of mounted circuit board including the given mounted circuit board are juxtaposed with narrow spaces.
In this case, a mirror driving mechanism provided with a mirror is inserted in a narrow space between the given mounted circuit board and an adjacent mounted circuit board, while a current is supplied to the given mounted circuit board from an electric power source. However, when the mirror driving mechanism is formed of an electric conductive material such as iron or aluminum, a short circuit may occur on the surface region of the current-supplied given mounted circuit board which may be destroyed.
A method for taking out a light from an object in a narrow space by means of a single optical probe to capture an image of the object is shown in a Japanese Patent Application KOKAI Publication No. 07-360. The optical probe used in the method shown in this publication has a narrow view angle and narrow view range of an image to be captured. When it is desired to capture an image of a part laid outside of the view range, the position of the optical probe or the optical axis of the optical probe should be moved to face the optical probe with the object. The position of the probe and the direction of the optical axis of the optical probe may be moved by hand or by changing the tension of a steel wire coupled to the optical probe. However, such a structure and a method for handling to realize this method are complicated and require much time to capture the image. Particularly, it is not possible to obtain a temperature distribution image of a wide range correctly at the same time.
Further, a method of detecting a temperature distribution image for a wide range by moving a mirror inserted in a narrow place is disclosed in a Japanese Patent Application KOKAI Publication No. 2002-206968. However, this method also requires an actuator for driving a mirror to render a structure and handling for realizing this method are also complicated and the operation for detecting the temperature distribution may be restricted.
Further, when a mirror and the like is driven in the narrow space for capturing a temperature distribution image, the air in the narrow space will be stirred. As a result, a local cooling or local heating will be occurred with respect to the surface of the object in the narrow space that it is not possible to obtain a correct temperature distribution image. Further, when a frame of a mirror or the like is moved within the narrow space between the two adjacent circuit boards, there is a possibility of occurring disadvantages such as a short-circuiting of the mounted electrical parts on the circuit board which causes the destruction of the circuit board.
This third method is also restricted by the size or weight of the mirror inserted in the narrow space and cannot be used to obtain a wide range visible image or a wide range temperature distribution image at the same time as in the first method. When a temperature distribution in the narrow space is detected, an infrared light radiated from an object to be detected should be merely detected. However, when a visible image is detected, it is necessary to irradiate the object to be detected by a visible light. To this end, a separate optical cable system for irradiating the object is necessary in addition to the optical cable for the infrared image detection optical probe. As a result, the total diameter of the optical cable becomes large so that it becomes difficult to insert such the thick optical cable into the narrow space. Further, a plurality of optical fibers to be connected to the optical probe becomes necessary in order to increase the resolution the obtained image.
Accordingly, since a range of view to be detected is restricted in the conventional methods, it is necessary to move an optical probe or the mirror in a narrow space for obtaining a wide range temperature distribution image or a wide range visible image. In other words, it is not possible to obtain the wide range temperature distribution image or the wide range visible image at the same time without moving the optical image or the mirror. Therefore, when the temperature distribution image or visible image changes frequently in a short period of time, it is not possible to obtain the images correctly.